The present invention relates to a liquid fuel injector for burners in gas turbines.
As is known, gas turbines are machines which consist of a compressor and of a turbine with one or more stages, wherein these components are connected to one another by a rotary shaft, and wherein a combustion chamber is provided between the compressor and the turbine.
In order to pressurise the compressor, it is supplied with air obtained from the external environment.
The compressed air passes through a series of premixing chambers, which end in a nozzle or a converging portion, into each of which an injector supplies fuel which is mixed with the air, in order to form an air-fuel mixture to be burnt.
There is admitted into the combustion chamber the fuel which is necessary in order to produce the combustion, which is designed to give rise to an increase in the temperature and enthalpy of the gas.
Subsequently, via corresponding ducts, the high-temperature, high-pressure gas reaches the turbine, which transforms the enthalpy of the gas into mechanical energy which is available to a user.
Between the compressor and the combustion chamber there is provided a series of burner units, the functions of which include supplying the liquid fuel, obtained from a remote tank, to the combustion chamber.
Known burner units have a complex structure, inside which there is present an injector, contained in a converging body, which in the technical language is generally known as the shroud.
In turn the injector, which, it will be appreciated, is connected to a supply duct for the liquid fuel, generally has a body which is provided with a cylindrical portion and a pointed end portion.
The liquid fuel injectors for burners in known gas turbines have a duct which is used in order to permit passage of the fuel, and are provided with ducts for the inflow of compressed air from the compressor of the turbine.
Both the duct for the fuel and the ducts for the compressed air end in corresponding outlet holes, wherein the air output from the injector is used to vaporise the fuel in order to improve the characteristics of the combustion.
In addition, there is associated with the converging body an element which is generally known according to the art as the swirler, which is used to intercept the flow of air obtained from the compressor, and has a complex shape, consisting of two series of blades, oriented in opposite directions, which are designed to produce a turbulent flow of the compressed air obtained from the compressor, thus permitting corresponding mixing of the air itself with the liquid fuel injected by the injector into the pre-mixing chamber.
Problems which occur particularly in the technical field of burners concern the need to obtain optimum atomisation of the liquid fuel, as well as mixing which is suitable for the different characteristics of the fuels used.
In addition, it is desirable to avoid unwanted return of the flame towards the burner, which leads to the machine being switched off.
Finally, it is desirable to obtain optimum conditions of turbulence of the fluids present in the pre-mixing area, and to reduce the emission of by-products of the combustion, and in particular pollutants such as nitric oxides.
The object of the present invention is thus to provide a liquid fuel injector for burners in gas turbines, which has an extremely simple and compact structure, whilst maintaining optimum fluid-dynamic characteristics, as previously described.
Another object of the invention is to provide a liquid fuel injector for burners in gas turbines, which permits optimum reliability of use of the machine.
Another object of the invention is to provide a liquid fuel injector for burners in gas turbines, which can be produced at a low cost, and consists of a reduced number of component parts.
These and other objects are achieved by a liquid fuel injector for burners in gas turbines, of the type used inside burners which are provided with a pre-mixing chamber and an element to create turbulence in the flow of compressed air obtained from the compressor of the said gas turbine, the said injector comprising a body which ends in a tip and is provided with at least one duct for passage of the fuel, and ducts for the inflow of compressed air from the compressor of the said turbine, wherein the said duct for the fuel and the said ducts for the compressed air end in respective outlet holes, characterised in that the tip of the said injector ends at the median part of the converging portion of the said pre-mixing chamber.
According to a preferred embodiment of the present invention, the holes for lateral discharge of the compressed air are located downstream from the holes from which the liquid fuel is discharged.
In addition, the centre of each of the holes for lateral discharge of the compressed air is located on a line parallel to the axis of the injector, relative to the corresponding hole for discharge of the liquid fuel.
According to a preferred embodiment of the present invention, the holes for lateral discharge of the compressed air, and the holes for discharge of the liquid fuel, are located downstream from the element for the turbulence, and in a position which is clearly separated from the latter.
According to another preferred embodiment of the present invention, the body of the injector has a plurality of intake ducts, in order to permit intake of the compressed air from the said compressor.
According to a further preferred embodiment of the present invention, inside its own tip the injector has a duct which is in communication with the ducts for passage of the compressed air, and ends in a hole, from the front of which the compressed air is discharged.
In addition, the injector according to the present invention is provided with a tube, which is outside the one for supply of the liquid fuel, and acts as a thermal insulator. The two tubes are kept equally spaced from one another by means of a corresponding spring.
Further characteristics of the invention are defined in the claims attached to the present patent application.